Which factor is most likely to influence ventilation effectiveness beyond the designed outdoor air supply?

• A. Exterior color and patching
• B. Filtration only
• C. Air distribution, leakage, and filtration
• D. Site orientation

Answer: (C)

Ventilation effectiveness is about how air actually moves through a space and how well it is cleaned, not just how much outdoor air is promised by the system. Even with a designed outdoor air supply, the real performance depends on three interconnected factors: how the air is distributed by the ducts and diffusers (whether it reaches all occupied areas evenly or creates stagnant zones), how leaks in ducts and the building envelope alter the air path (short-circuiting or bypassing the intended delivery reduces the fresh air reaching occupants), and how filtration affects pollutant removal as air travels through the system (removing particles but not fixing poor distribution or leaks if air isn’t circulating well). If the airflow is poorly distributed, or if leaks divert air away from the breathing zones, the occupants may still experience low air quality despite the target outdoor air rate. Filtration helps, but it can’t compensate for bad distribution or significant leakage. Exterior color, patching, or site orientation can influence outdoor conditions, but they do not impact interior ventilation effectiveness as directly as the combined effect of distribution, leakage, and filtration.